1. Field of the Invention
The invention relates to a converter for changing given first and second variables, which correspond to the angle coordinate and the magnitude coordinate of a vector defined in polar coordinates, into third and fourth variables which correspond to the Cartesian coordinates of the vector.
2. Discussion of the Prior Art
A coordinate converter for changing polar vector variables into Cartesian vector variables is needed for various purposes, for instance, for testing computer modules such as a vector analyzer (as shown, for instance, in German Pat. No. 1 941 312, FIG. 5) and a vector rotator (for instance, German Pat. No. 1 941 312, FIG. 6), or for checking circuits which use such computer modules. Another application is, for instance, the frequency-independent generation of firing angle for controlling the electric valves of a converter (see, for instance, German Auslegeschrift No. 2 620 992, FIG. 1, for the formation of variables e1 and e2). The requisite coordinate converter should be capable, if the polar coordinates (magnitude and angle) of a vector are given, of forming the Cartesian coordinates of the vector, the one coordinate axis being identical with the reference axis for the angle.
In Siemens-Zeitschrift 45 (1971), no. 10, pages 757 to 760, especially FIG. 7 on page 759, a computing circuit is described which forms two output variables a1 and a2 from three input variables sin .alpha., cos .alpha. and a. Here the two input variables sin .alpha. and cos .alpha. represent the angle .alpha. and the input variable a represents the magnitude of a given vector. The output variables a1 and a2 represent the Cartesian coordinates of this vector. In this case, the computing circuit consists of two multipliers; adders are not required. In the known computing circuit, however, the two input variables, sin .alpha. and cos .alpha., i.e., two trigonometric functions of the angle .alpha., must be given. The trigonometric functions must be generated, for instance, by two function generators, which, given the usual accuracy requirements, requires a large expenditure of means. It is therefore desirable to avoid such function generators.
It is an object of the present invention to provide a coordinate converter of the type mentioned above for processing a vector and, which needs only two input variables while, nevertheless, being distinguished by the small amount of hardware required. The coordinate converter should therefore make it possible to calculate from the polar coordinates of a given vector the corresponding Cartesian coordinates.